Upper Permian ostracode assemblage from the Jadar Block ( Vardar Zone , NW Serbia )

Ostracodes from the Changhsingian (latest Permian age) in the uppermost part of the “Bituminous Limestone” Formation of the Komirić Section in NW Serbia (Jadar Block, Vardar Zone) are described and illustrated. Three new species of ostracodes are introduced: Basslerella jadarensis n. sp., Acratia serbianella n. sp., and Knoxiella vardarensis n. sp. The ostracode assemblage, together with conodonts and foraminifers, is the first record of the youngest Late Permian age microfaunas from Serbia and from the central part of the Balkan Peninsula.


Introduction
The Permian and Triassic deposits widely distributed in the Jadar Block area (NW Serbia) have been the subject of numerous geological investigations.Among these strata, sediments belonging to the Permian-Triassic (P-T) boundary interval, represented by shallow-water marine carbonates with different fossil associations and specific characteristics of the depositional environments, are unique in Serbia.They lack ammonoids, but diverse Upper Permian macroand micro-assemblages (brachiopods, bivalves, gastropods, algae, foraminifers, etc.), and a poor Lower Triassic microfossil association (foraminifers, ostracodes) have been determined.
During long-term geological investigations, particularly in NW Serbia, the Serbian authors of this paper collected many samples for palaeontological and sedimentological analysis.The main interest was to confirm the presence of conodonts in Palaeozoic and Triassic sediments, especially in the P-T interval beds.Additionally, with these intensive geological studies of NW Serbia, the authors intended to document palaeontological, biostratigraphical, and sedimentological data in order to refine the existing lithostratigraphical definitions.
These investigations resulted in several important papers on the Variscan and Early Alpine evolution of the Jadar Block (FILIPOVIĆ et al. 2003), Late Pennsylvanian conodont biostratigraphy and sedimentology (SUDAR et al. 2007b) The current investigation represents a continuation of the above mentioned studies.In this paper, the Upper Permian ostracode fauna, not only from NW Serbia, but also from the whole of Serbia and the central part of the Balkan Peninsula is determined for the first time.From these regions, only PANTIĆ-PRODANOVIĆ (1979) mentioned "Campilian" ostracodes in the vicinity of Valjevo, and KRSTIĆ (1980) reported the ostracode fauna of the same age from the Gučevo Mt.
The ostracodes described and illustrated herein were found in samples taken from the Komirić section in the Vlašić Mt. region of NW Serbia.They occur together with conodonts and foraminifers in the uppermost part of the "Bituminous Limestone" Forma-tion from the lower part of the section (SUDAR et al. 2007a, NESTELL et al. 2009).

Geological setting
The Jadar Block, situated at the southern margin of the Pannonian Basin, covers almost the whole area of NW Serbia and southern Srem (Vojvodina).Westwards, it extends beyond the Drina River to eastern Bosnia (Fig. 1A).
This tectonostratigraphic unit is today an exotic block terrane within the Vardar Zone.It is surrounded by the Vardar Zone Western Belt, except on the farthest south-eastern part where it is in direct contact with the Kopaonik Block and the Ridge Unit, which is also a part of the Vardar Zone (Fig. 1A).Unlike the Vardar Zone Western Belt, the absence of post-Early Jurassic sediments, ultramafites, ophiolitic mélange, and Cretaceous flysch development is evident in the Jadar Block (FILIPOVIĆ et al. 2003).
In the Jadar Block, the deposition occurred during the Variscan and Early Alpine evolution with a predomination of Dinaridic features.

Komirić Section
The Komirić Section is located on the north side of the Valjevo-Loznica road, in the Komirić Village, on the southern slope of the Vlašić Mt. (GPS coordinates x 4918588, y 7985697, Fig. 1).About 78 m of marine carbonates of Late Permian and Early Triassic age are exposed in this site, but only 19 m of the column were sampled for microfauna.The lower part of the outcrop consists of 7 m dark grey and black, massive to thick-bedded bituminous bioclastic limestones belonging to the "Bituminous Limestone" Formation (Fig. 2).Abundant   foraminifers, algae, ostracodes, conodonts, holothurian sclerites, crinoids, echinoids, brachiopods, gastropods and ophiuroids occur.After a fault, marked with 15 cm-thick breccia, there are 12 m of the thick-tothin bedded light grey and grey fine crystalline limestones (wackestones) with stylolites and laminae in certain levels.Occurrences of dolomitic limestones are less frequent.These latter limestones contain very rare indeterminable specimens of ostracodes, foraminifers and different parts of echinoids, and belong to the Svileuva Formation, which in Fig. 2 represent only 5.5 m of the column.

Ostracode fauna
Nine samples from the Changhsingian (Late Permian), processed for conodont study by 15-17 % acetic acid digestion, gave a poorly preserved ostracode fauna.However, it is the first time that ostracodes of this age have been discovered in Serbia and it is an important step in the knowledge of the distribution patterns of Upper Permian ostracodes.
Thirty eight species, including three new ones, belonging to 18 genera were distinguished: Oliganisus? sp.Type locality.Komirić Section, Komirić Village, southern slope of the Vlašić Mt., NW Serbia.
Type level.Bed 2, sample MS 1181, 3.80 m at the base of the "Bituminous Limestone" Formation exposed in the Komirić Section, uppermost Permian, Changhsingian.
Diagnosis.A species of Knoxiella with a blade ridge on L3.
Description.Carapace subrectangular with straight DB; AB regularly rounded with maximum curvature located at mid height; VB regularly rounded; PB with medium radius of curvature and maximum convexity located at the upper third of height; ACA = 140-145°; PCA= 130-135°; free margins flattened; L2 poorly expressed; S2 deep, with lower part located between upper third and mid height; L3 large and clearly marked with a ridge in blade form on the dorsal part, its upper part extends beyond DB; maximum of height located between the anterior third and mid length; no secondary ornamentation observed.Sexual dimorphism expressed by a thickening of posterior part of the carapace in heteromorphs.RV overlaps slightly LV on free margins Remarks.Knoxiella vardarensis n. sp. has the same outline as Knoxiella infirma SHI, 1982 from the Late Permian of South China and Turkey (CHEN & SHI 1982;CRASQUIN-SOLEAU et al. 2004).Here, the free margins are more flattened and there is a ridge on the dorsal part of L3.A similar ridge is present in some Sargentina species, such as Sargentina pamucakensis CRASQUIN-SOLEAU, 2004 or Sargentina transita (KO-ZUR, 1985), but the overlap, of course, differs completely between Knoxiella and Sargentina.
Diagnosis.An elongated species of Acratia with a reversed overlap and a large radius of curvature at AB.
Description.Carapace elongated (H/L = 0.33-0.38);RV overlaps LV; overlap weak all around the carapace with the maximum at VB; AB with quite large radius of curvature for the genus; AVB straight and horizontal; acratian beak clear but not pronounced; VB slightly convex to straight on the RV, straight to gently concave on the LV; PB tapering; PDV and ADB straight on both valves; carapace thin, biconvex with a maximum of width at mid L.
Remarks.Acratia symmetrica HAO, 1992 and Macrocypris cf.menardensis HARLTON sensu SHI & CHEN, 1987 have the same reversed overlap but have a different outline.Acratia oliverifera CHEN sensu HAO, 1994 (the species figured by HAO (1994) is not A. oliverifera CHEN, 1958) has a similar outline but here the acratian beak is less pronounced.Acratina goemoeryi KOZUR, 1970 from the Upper Anisian is the closest species but has a straighter DB and a smaller radius of curvature at AB. Acratia n. sp. 1 sensu CRASQUIN et al. 2004 from the Upper Permian of Turkey (Western Taurus) is questionably included in the new species.The uncertainty comes from the fact that the Turkish specimens are not so well preserved.
Diagnosis.A species of Basslerella with a relatively high carapace (H/L = 0.72), small radius of curvature at AB and straight DB.
Description.Carapace relatively high (H/L = 0.72); DB straight at RV and convex at LV; AB rounded with a quite small radius of curvature and a maximum convexity located at the lower third of H; VB nearly straight; PB relatively angular with postero-dorsal part quite vertical; maximum H located a little anterior of mid-L; LV overlaps RV all around the carapace; dorsal view biconvex with a maximum thickness located in the posterior part.
Remarks.Basslerella annesophieae CRASQUIN, 2010 from the Early-Late Permian of South China and South Alps is quite close to the new species but has an AB with a larger radius of curvature.
Basslerella firma KELLETT, 1935 and B. obesa KEL-LETT, 1935 from the Early Permian of Kansas (USA; KELLETT 1935) both have a more elongate carapace (H/L = 0.60) and a more narrowly rounded AB.

Comments on the ostracode fauna
Three species present here are known in other areas.Acratia visnyoensis KOZUR, 1985 is known in the Wuchiapingian, the late Permian of the Bükk Mountains in Hungary (KOZUR 1985), in the Wordian-Wuchiapin-gian of western Taurus, Turkey, (CRASQUIN-SOLEAU et al. 2004) and in the Changhsingian, Late Permian of the Meishan Section, Zhejiang Province, South China.
?Paraparchites chenshii CRASQUIN, 2010 is known from the latest Changhsingian of the Meishan Section in South China (CRASQUIN et al. 2010).The presence of these three common species demonstrates the palaeobiogeographical links between south-eastern, central and northern parts of the Palaeo-Tethys during the Late Permian.
Ostracodes are predominantly benthic inhabitants and, therefore, reflect sea-floor conditions.Different families had specific palaeoecological preferences.All the forms recognized here are characteristic of intertropical warm waters.Almost all specimens are represented by closed carapaces.This indicates limited transport and/or burial in a soft substratum (OERTLI 1971).Such preferences of the Late Palaeozoic-Early Triassic ostracode families may be summarized as follow (LETHIERS 1982;MELNYK & MAD-DOCKS 1988): -internal zone with variations of palaeoenvironmental conditions (bathymetry, salinity), Kloedenelloidea, Kirkbyoidea, Hollinoidea (group 3 in Fig. 4); -median zone with euryhaline environments in shallow to very shallow waters: Paraparchidoidea, Cytherideidae, Cavellinoinidae (group 2 in Fig. 4); -external zone, open carbonate environments with normal salinity: Bairdioidea (group 1 in Fig. 4).
The respective percentages of the three groups are presented in Fig. 4.This representation shows that all the assemblages analysed here are, on the whole, typical of a platform environment with a depth of less than 50-100 m.Four levels contain ostracode assemblages that group three families, which testify to a more internal zone (samples MS 1203/1, MS 1181, MS 1184 and MS 1186/1).-0011).This is a contribution to the IGCP-Project 572 ("Recovery of ecosystems after the Permian-Triassic mass extinction").We thank ALEXANDRE LETHIERS (UPMC, Paris) for the preparation of some figures and the SEM microphotographs.Authors thank to reviewers ALAN FORD (Frankfurt) and MATEVŽ NOVAK (Ljubljana) for the critical and constructive comments.